Since it's a societal problem, but solved on the microlevel of one person at a time, it seems the way to have a broader effect is to show the value of having connection with other people over the value of not.

Overcome any addictions (scrolling, gaming, etc.) that stand in the way would be easier if the goal was clear.

Overcoming attitudes and defensive beliefs (too many cliques, they won't talk to me...) go away when you can either recall a time when you had friends or know others who do.

Convince people it's better (in their own value system) to be social, have friends of all kinds, and let them know their value and meaning increase by being a friend, I think you'd have a hard time stopping people from becoming social.